Author
P.G. ASTERIS and A.D. TZAMTZIS
Technological Educational Institution of Athens

Abstract
A new methodology for the non-linear macroscopic analysis of unreinforced masonry (URM) shear walls under biaxial stress using the finite element method is presented. The methodology focuses on the definition / specification of the yield surface for the case of anisotropic masonry under biaxial stress, as well as on the numerical solution of this non-linear problem. Specifically, in order to define the yield surface, we use a cubic tensor polynomial, and apply the initial stress method in order to solve the elasto-plastic problem. In addition, a novel computer code of finite elements has been developed in order to implement the proposed method of analysis. The main advantage of the method is that the formulation of the plasticity equations through a regular yield surface leads to the elimination of the problem that occurs by the use of a singular surface. Furthermore, it is clearly shown that the non-linear behaviour of URM is strongly affected by the yield criterion used.